Here's the Conservatives' nightmare, and the squishy left's wet dream. There's a hung Parliament, perhaps with Labour soundly beaten into second or even third place yet clinging onto their status as the single largest party. Gordon Brown and Nick Clegg do a deal: full proportional representation, alongside sundry other constitutional tinkerings. The referendum is carried. Result: permanent centre-left government. "The danger facing the Conservatives is existential" thinks Ben Brogan. While Guido brings us a panicky email from Peter Bingle of PR firm Bell Pottinger:
If David Cameron does not become PM on 6/7th May the electoral system will be changed. The first past the post system will be abolished and there will not be a Tory government for a very long time if ever again. Perhaps John Major will go down in history as the last Tory PM.
These gloomy assumptions spring from the unstated belief - perhaps gleaned from paying too much attention to the output of the BBC - that Britain has a permanent left-wing (or at any rate "progressive" majority) and that, therefore, it is only the Labour-Lib Dem fracture, combined with the minority-rule that comes with First Past the Post, that allows the Conservatives ever to form the government.
Would a changed voting system really sink the Tory party, though?
Imagine that PR had been in place at the last general election in 2005. Labour would have been considerably short of a majority and with not much more than 35% of the vote there would have been a strong case that it had been rejected by the electorate. The Lib Dems might have propped up Tony Blair (if only as a more attractive proposition than Michael Howard) but they would have extracted some serious concessions - killing off ID cards, perhaps. At any rate, it couldn't have been worse than the past five years.
Now fast-forward to today. The coalition has struggled on to the end of the Parliamentary term, but - buffeted by recession and revelations of the way many MPs have abused the expenses system - it has become deeply unpopular. Charles Kennedy was forced to resign as foreign secretary and party leader after an incident at a Brussels summit at which he appeared to be incapable. The Chancellor, Vince Cable, is widely regarded as a doomsaying misery-guts. His rows with Gordon Brown are legendary and with the two at loggerheads economic and fiscal policy has become deadlocked. Few believe the coalition could last much longer, even without the election. Indeed, many express astonishment that it has survived as long as it has, given the contrast between the two parties. Since most Blairites were swept away in 2005, Labour has returned to a semblance of traditional socialism. The Miliband brothers, while still loyal to the coalition, are standing at the election under Liberal colours.
The Conservatives, meanwhile, as the only major party untainted by incumbency, were able to sell their message of change to a disillusioned public - among them many former Lib Dems unimpressed by their party's support of a discredited prime minister. Other voters - including many young people - have signalled their intention to vote Green. After Caroline Lucas was controversially allowed to participate in one of the leaders' debates one opinion poll put Green support at almost 30%. Wilder commentators speculated that they might become the second largest party in the new Parliament. It's certainly quite possible that they will hold the balance of power. David Cameron, it had been noted, has increased his environmental rhetoric recently as a part of a "love bombing" strategy, though the post-debate polls brought panic in Tory ranks, with senior members of the shadow cabinet touring TV studios to explain how the Green manifesto, if implemented, would prove economically ruinous.
In the end, the Green surged subsided, as anti-government feeling coalesced around the Conservatives. UKIP also put up a strong showing, as did some independent candidates who were forced by the system to stand under a collective banner - Society, Trust and Liberty (or, as one wag adapted it, Sod The Lot). While the Tories' 41% put them short of an overall majority, David Cameron managed to cut a deal with the DUP and UKIP (Nigel Farage accepting a post as health secretary, much to his own amusement) and the independents signalled that they would respect what everyone agreed was a public desire for a new government. So David Cameron walked into 10 Downing Street.
The big losers, it turned out, were the Liberal Democrats. Tainted by their association with Labour, and widely seen as fractious and incoherent, the party split. One faction, led by Chris Huhne, joined the reduced Labour benches. The other, restyling itself the Liberal Party and led by a young ex-public schoolboy by the name of Nick Clegg, signalled that it saw its long-term future as in a loose alliance with the Tories. Many on the traditional Left vowed that they would never forgive Blair for agreeing to voting reform - which, they reasoned, had doomed the Labour Party to long-term oblivion. The future, they gloomily predicted, would be one of almost permanent centre-right government.
They were, of course, wrong.